This invention relates to a logic analyzer and especially to an apparatus for detection and measurement of unwanted signals commonly referred to as glitches.
A logic analyzer that analyzes the operation of a logic circuit usually contains in it a cathode ray tube (CRT) to display the waveforms which obtain at various points of the logic circuit under test, so as to allow the user to know whether the logic circuit works correctly or not. Such systems are discussed for instance in Understanding Logic Analyzers, by Roy Tottingham, in Machine Design, Apr. 12, 1979. In recent logic analyzers a glitch detection circuit is also provided, and from the waveforms shown on the CRT a glitch may be recognized by the user, for instance as described in U.S. Pat. No. 4,107,651.
In such a prior art glitch detection circuit, although it is possible to detect a glitch, it is not possible to measure the width of the glitch. Information on the width of the glitch is useful for finding the cause of the glitch, for knowing the propagation time delay of the circuit and so forth.
A glitch that is superimposed on digital data is usually a very narrow pulse that is sometimes periodic and sometimes not periodic. Thus, measurement of the pulse width of glitches by for example a counter or some other time-interval-measuring instrument is difficult. There is a possibility of measuring a glitch width by using an oscilloscope along with a logic analyzer contained in a glitch detection circuit. When a glitch is detected in a certain position of the data train by the logic analyzer, the user adjusts the oscilloscope to obtain suitable triggering to observe the waveform of the glitch. However, this operation is complicated and difficult. Further, since both a logic analyzer and an oscilloscope are required in this method, it becomes quite expensive.